When an abnormality occurs, for example, when a current excessively flows through an electrical apparatus (for example, a motor) thereby causing the electrical apparatus to reach an abnormally high temperature or when the electrical apparatus reaches an abnormally high temperature due to some reason other than the excessive current, it is needed to secure a safety of the electrical apparatus by interrupting the current flowing through the electrical apparatus and eliminating the abnormality as necessary. A bimetal component is used as a means to interrupt such current.
A bimetal component comprises a sheet member of bimetal metal. The bimetal component is configured to activate (i.e. deform) and interrupt a current flowing through the bimetal component when the bimetal itself reaches a high temperature in excess of a particular temperature, or when the bimetal reaches a high temperature in excess of a particular temperature due to a rise in the temperature of an ambient atmosphere.
When such bimetal component is incorporated in an electrical apparatus, the bimetal component activates when the electrical apparatus reaches an abnormal temperature due to an excessive current or some other reason and interrupts the current. The temperature of the electrical apparatus decreases by an interruption of the current, and the temperature of the bimetal component also decreases so that the bimetal component returns to its original shape (i.e. resets), and as a result, the current may be allowed to flow again before the safety of the electrical apparatus is secured.
In order to prevent the current from flowing again in this manner, it is necessary to ensure and maintain the state when the bimetal are activated. For this purpose, the bimetal component is disposed in series in the circuit of the electrical apparatus to interrupt the circuit current, while at the same time a PTC component is disposed in parallel to the bimetal component. By such arrangement, when the bimetal component is activated, the current flowing through it is diverted to the PTC component; the PTC component generates a Joule heat by the current and this heat is transmitted to the bimetal component so that the activated state of the bimetal component may be ensured.
A protection device which is configured so that the bimetal component is disposed in series in the electrical circuit and the PTC component is disposed in parallel to the bimetal component is known. Such protection device is disclosed, for example, in the Patent Reference 1 shown below. In such protection device, a resin base having terminals comprises a PTC component, a bimetal component and an arm within a space provided in the resin base; a cover which is previously provided with an upper plate is placed on the resin base, and the resin base and the resin cover in this state are bonded with an adhesive or by ultrasound fusion.
Japanese Publication No. JP 2005-203277 is a prior patent reference.